1. Field of the Invention
Although many insects have the ability to fly to their host plants, others must walk because they do not have wings, or because their wings are not functional at certain stages of their adult life or because environmental conditions preclude flight. A good example is beetles, e.g. the Colorado Potato Beetle (CPB), Leptinotarsa decemlineata, which is the most important insect pest of tomatoes and potatoes in North America and parts of continental Europe and Asia. This pest can decimate entire fields, and has become resistant to almost all registered insecticides in some areas. These beetles fly or walk to the perimeters of potato or tomato fields at the end of the growing season, and bury themselves into the soil in protected areas to survive the winter. In the following spring, the adults emerge from the soil, and seek new plantings of potato or tomato. At this time, their flight muscles have atrophied to the state that they generally do not fly for 5-7 days, and must walk to find host plants. A common occurrence is that they leave the headland areas surrounding the previous year's crop, and walk to the nearest new plants. This usually results in the outer rows of new plantings being heavily infested.
2. Description of the Prior Art
Where insecticide resistance has occurred, as in parts of Canada and U.S.A., growers have resorted to a number of novel pest management strategies. When potatoes are small, and when the beetles first arrive in the crop, tractors fitted with specially designed propane flamers are used to kill adults on the plants. The damaged potatoes are small enough to recover from the effects of the heat. This technique can only be used early in the growing season, however, to avoid severe damage to the larger plants. Growers have also used vacuum suction devices to remove adults and immature stages from the plants. Such devices are expensive, slow moving, and not completely effective. Taking advantage of the fact that most beetles walk from the field edges into the crop, growers have been instructed on how to mass trap them using plastic-lined trenches, e.g. as described by Gilles Boiteau et al (1994) "Development and Evaluation of a Plastic Trench Barrier for Protection of Potato from Walking Adult Colorado Potato Beetles", J. Econ. Entomol. Vol. 87, no. 5: 1325-1331. Essentially, machinery has been developed that digs a smooth trench around the edge of the field. During the process, a device has also been developed to line the trench with black plastic, which is covered at both sides with soil to keep it in place. The beetles walk to the trench and upon entry, cannot climb out. Photos of the trench show that it is quite effective in catching beetles, which quickly die from the heat build-up in the black plastic lined trench. This latter technique has been adopted by several growers in areas of Canada desperate for a means of controlling this serious pest. It is estimated that an average of 50% of incoming beetles are intercepted by the trench, which may go as high as 80% in some cases.
Several drawbacks have been observed with these alternate control strategies. With the plastic lined trenches, a major drawback is that growers must purchase the trenching apparatus and install the trenches. Also, the trench will have variable results, depending on how well the plastic has been installed, and on other factors such as weed growth and tearing of the plastic. In some cases, wet field conditions have prevented the installation of plastic trenches before substantial immigration of beetles has occurred. At the end of the growing season, the growers also face the problem of removing and disposing of the plastic, which cannot be re-used.
Insect barriers are also described in prior patents, such as the snail barrier described in U.S. Pat. No. 5,170,584, issued Dec. 15, 1992. The primary purpose of this device is to provide a safe place for presenting toxic material to the snails that is virtually free from the risk of accidental poisoning of pets and children. Poisonous baits are placed in a trough and the trough is oriented such that it is occluded from both visual and tactile access thereby precluding access to the poisonous bait by non-target organisms. However, this barrier would not be suitable for beetles because they would be incapable of crawling into the region containing the bait. Also, any barrier device that will not collect and kill the beetles would only serve to temporarily delay them, since they would eventually find alternate routes into the field (i.e. by eventually being able to fly over the barriers).
U.S. Pat. No. 2,054,730 shows a roach trap in which ramps are provided such that the roaches climb up the ramps and fall into a box-like receptacle. However, many species of beetles will not climb over a sharp edge and fall into a receptacle, so that the trap of U.S. Pat. No. 2,054,730 would not be useful for trapping CPB beetles.
Another insect trap is described in U.S. Pat. No. 2,100,966. This trap comprises a base, side and end walls, with the side walls being inclined upwardly from their ends and downwardly to form V-shaped portions at their middles. Sections of wire fabric secured to the walls have their adjacent ends terminating in the V-shaped portions. Entrance openings are provided in the V-shaped portion through which the insects can crawl and enter the trapping chamber. The insects are enticed through the entrance openings and into the chamber by bait placed within the chamber. However, the device will not work against Colorado potato beetles, because there are no suitable lures to place inside the device, and the wire fabric walls would stop them from slipping and falling into the structure. The beetles would be able to easily climb over the device.
It is the object of the present invention to provide a simple design of portable barrier capable of precluding migration and confining agricultural pest insects, e.g. beetles, so that entry into cultivated areas is blocked.
It is a further object to provide a portable barrier that can selectively retain insects.
It is a still further object to provide a portable barrier that can be left in place throughout a growing season, while being easily convertible between an insect collecting mode and a non-collecting mode.